This invention relates to a multi-pole load break switch having two sets of ganged contacts in each pole connected in series to isolate its fuse and to a circuit incorporating said switches in doubled-ended switch boards or anywhere there may be a current backfeed.
Fused load-break, multi-pole switches are frequently used as service entrance equipment and in other relatively high current applications. When installed in hospitals or in other facilities where the continuity of electrical service is essential, a dual power supply is usually provided so that if one power main is shut down the electrical load can be handled by the other power main. In such a conventional dual source installation, each power main normally supplies its own group of branch circuits with the two power mains tied between the groups of branch circuits by a normally open fused load-break, multi-pole switch. In such a circuit, all of the fuses are normally "hot". If, for any reason, one of the power mains fails or must be shut down, its load break switch is opened and the load break switch in the tie between the power mains is closed, thereby supplying power from the other power main to both groups of branch circuits. After the closing of the load break switch in the tie, all of the fuses, including the fuse for the power main that was disconnected or shut down, remain "hot". In such circumstances an electrician must either change a fuse under "hot" conditions or, if such a procedure is considered too dangerous under the circumstances, the entire electrical service to the facility must be shut down in order to safely replace a fuse, thereby frustrating the purpose for which a dual source of power was originally provided.